Process for the electrochemical production of olefin oxides



United States Patent US. Cl. 20479 9 Claims ABSTRACT OF THE DISCLOSURE Electrochemical conversion of olefins to their corresponding oxides in an electrochemical cell having an anode, a cathode and a textile diaphragm therebetween,'- wherein the diaphragm is a fabric having a resistance to liquid flow therethrough of about 2 to 60 kg. per hour per drn. of area of a S-percent aqueous potassium chloride solution at a temperature of about 20 C. and a pressure differential of about 200 mm. Water.

This invention relates to a process for the electrochemical production of olefin oxides. More particularly, the present invention relates to new materials particularly suitable as diaphragms in such a process.

It is known that olefin oxides can be produced from olefins by an electrochemical process comprising electrolysing an aqueous solution of a metal halide in an electrochemical system, introducing the olefin into the reaction system in the vicinty of the anode, and dehydrohalogenating the halohydrin initially formed in an electrochemical system to form the olefin oxide (cf. Belgian patent specification No. 637,691 and French patent specification No. 1,375,973). In particular, the process is carried out by passing the electrolyte from the anode compartment through a diaphragm into the cathode compartment, in which case an olefin halohydrin is formed from the olefin introduced into the anode compartment under the electrochemical effect, transferring the olefin halohydrin dissolved in the electrolyte through the diaphragm and converting in the cathode compartment the olefin halohydrin into the olefin oxide under the effect of the alkaline conditions prevailing therein. Several of these systems consisting of anode, diaphragm and cathode can be combined together to form a cell unit.

In this process, an inert material which is permeable or porous, for example, abestos, polyfluorohydrocarbons, polyethylene, and so on, can be used as the diaphragm which separates the anode compartment from the cathode compartment.

We have now found that it is of particular advantage to use diaghragms made from textile materials, preferably fabrics, which consist of thermoplastic fibres or filaments, or which have been produced from fibres or filaments coated with thermoplastic materials either b fore or after production of the fabric, and the resistance of which to liquid flow is such that f om 2 kg. to 60 kg. per hour and preferably from 3.5 kg. to 40 kg. per hour, of a 5% potassium chloride solution pass through them per dm. of their surface area at a temperature of and at an excess pressure of 200 mm. water column.

Thermoplastic materials suitable for the purposes of this invention include, for example, polyvinyl chloride or copolymers of vinyl chloride and vinylidene chloride, polyesters, polyamides, polyolefins, such as polyethylene and polypropylene, polyacrylonitriles and modified polyacrylonitrile (modacryls). Textile materials consisting of, or containing, polyacrylonntriles or modified polyacrylonitriles are particularly suitable for the process according to the invention. As already mentioned, the fabrics can be produced from fibres or filaments consisting of thermoplastic materials of this kind. It is also possible, however, to produce the fabric from non-thermoplastic materials and to coat it afterwards with thermoplastic materials of the aforementioned kind, in which case precautions have to be taken to ensure that the pores of the fabric are not excessively, or even completely, covered by the coating. It is also possible to start with non-thermoplastic filaments, to coat them with thermoplastic materials and then to process them into textile fabrics. In this context thermoplastic materials are compounds which can be deformed under the action of pressure and/or heat.

It is of advantage to obtain maximum compactness during the actual production of the textile material. Alternatively, the compact textile material already described may even be combined with woven or non-woven fabrics, optionally not as compact, in which case the less compact farbics may cover one or both sides of the compact materials or may be embedded between two compact textile materials.

In one particularly preferred embodiment of the invention, the textile materials showing the resistance to liqu d flow claimed in accordance with the invention are obtained by subjecting already very compact fabrics to a pressure and/or heat treatment until the textile material shows the desired resistance to flow. For this purpose, it is convenient, for example, to treat the fabric between two rotating rollers (calenders) at least one of which preferably heated to an elevated temperature, for example, from 10 C. to 150 C., and advantageously from 20 C. to C., below the softening point of the thermoplastic material of which the fabric is made or with which it is coated. For this purpose, the rollers are preferably adjusted in such a way that they have a linear pressure (kg/cm. roller width) of from 20 to 200, advantageously from 50 to 150. The rollers may rotate at the same or at different speeds. Alternatively, the pressure treatment may be carried out, for example, by pressing the fabric statically between two plates at least one of which is preferably heated. It is also possible to pass heated, pressure-loaded plates over the fabric. Both sides, or alternatively only one side, of the fabric may be subjected to the heat treatment under pressure, for example, by heating both the rollers or by heating only one of them. The fabric may be passed through the rollers one or more times; in the latter case, the same or different conditions may be applied during each run. Alternatively, the fabric may be heated to the temperature required for pressure treatment before the treatment is actually carried out, in which case there is no need to heat the means used to apply the pressure. The heat and/ or pressure treatment leads to a superficial sinter, optionally to incipient softening of the fibres. These changes in the structure of the fabric lead to a reduction in pore size, making the fabric more compact, and to a more uniform distribution of the fibres over the entire surface. The consolidation obtained produces a substantial increase in the resistance of the fabric to the flow of electrolyte therethrough.

Despite the considerable increase in the resistance to liquid flow, there is only a slight increase in electrical resistance. i.e. there is no appreciable drop in the energy yield of the electrolytic process. The choice of the conditions under which the pressure and/or heat treatment is carried out must be directed towards obtaining a considerable increase in the resistance to liquid flow without at the same time appreciably increasing the electrical resistance of the diaphragm.

In the case of fabrics which have been pressureand/or heat-treated on one side only, the treated or the untreated sides can be arranged facing the anode.

The same applies to the pressureand/or heat-treated compact fabric which is only covered on one side with less compact materials.

Suitable starting materials for the production of the olefin oxides include, in particular, gaseous monoolefins such as ethylene, propylene and butylenes, as well as halogenated mono-olefins such as allyl chloride, for example. Aqueous solutions of sodium or potassium chloride, for example, or mixtures thereof, can be used as the electrolyte. The concentration of the salts in the electrolyte may, for example, be between 2% and 20%, and with advantage between 3% and Both the anode and the cathode may be rectangular in shape, in which case the two electrodes can be arranged opposite one another in parallel. The anode may be porous so that the starting material to be introduced in the form of a gas can be diffused through the pores of the anode into the anode compartment. However, the anode may also be non-porous. In this case, the gaseous olefins can be introduced through a frit or a similar means of distribution arranged beneath the anode. The olefins may even be introduced by other methods providing they ensure fine distribution of the gas in the anolyte. Suitable anode materials include, for example, graphite or titanium coated with a thin layer of noble metals such as platinum, iridium, rhodium, ruthenium or mixtures thereof or oxides thereof or other conventional materials. The aqueous electrolyte is introduced into the anode compartment and is transferred through the diaphragm and the cathode into the cathode compartment, in quantities of, for example, from 10 cm. to 100 cm. per minute per drn. of cathode area. The catholyte issuing from the cathode compartment can be freed from the olefin oxide present therein, for example, by distillation, and returned to the anode compartment, thus closing the circuit. If secondary products formed during electrolysis have accumulated to a certain extent in the circulating electrolyte, it is of advantage to remove some of the electrolyte from the circuit and to replace it by fresh electrolyte. The process can be carried out, for example, at current densities of between 2 and 50 amperes/dm. of electrode area, with voltages of from 3 to 5 v. and at temperatures of from 30 C. to 90 C. Although it is with advantage carried out at normal pressure, the process may even be carried out at a slightly elevated pressure. The olefin throughput across the anode compartment can be adjusted for example, in such a way that between 5% and 95% of the olefin is reacted in a single pass. The anolyte containing the halohydrin may also, for example, be reacted outside the cell with the catholyte to form the olefin oxide, and the reacted mixture of anolyte and catholyte may be returned to the anode and cathode compartments, respectively.

The invention is illustrated by the following examples:

EXAMPLE 1 (a) An electrolytic cell with a 1.75 dm. titanium plate anode provided with a thin coating of platinum, was used. The anode was arranged opposite a stainless steel wiregauze cathode of equal surface area. A fabric produced fromendless polyacrylonitrile filaments was used as the diaphragm which covered the cathode.

This fabric was passed between two rollers which were kept at a temperature of 140 C. and which were pressed against one another under a linear pressure of 160 kg./cm. roller width. The rollers rotated at a uniform peripheral speed of 5.8 metres per minute. The changes which the fabric used underwent during the combined pressure and heat treatment, are identified by the following numerical data. The throughfiow of a 5% aqueous potassium chloride solution at room temperature through the diaphragm amounted to 152 kg./dm. per hour before treatment and to 46 kg./ (1111. per hour after treatment at an excess pressure on the pressure side of a 200 mm. water column. The electrolytic cell was filled with a 5% aqueous potassium chloride solution. 4 litres per hour of this solution were passed from the anode compartment through the diaphragm and the cathode into the cathode compartment. 45 litres per hour of a C -fraction containing 91% of propylene were introduced in gaseous form through a frit arranged at the lower end of the anode plate. By applying a DO. voltage between the anode and the cathode, an electric current was passed through the cell in such a way that a current density of 10.7 amperes/dm. of apparent anode surface was applied. The total voltage of the cell amounted to 3.6 v. The temperature of the electrolyte was 52 C. The cell worked at atmospheric pressure. 20% of the propylene passed through the anode compartment was reacted. The yields of reaction products present in the anode and cathode spent gas or catholyte were as follows, expressed as percentages of the current applied:

Reaction product: Yield percent Propylene oxide 89.0 1,2-dichloropropane 8.0 Propylene glycol 0.6 Propylene chlorohydrin 0.7 Other organic products 0.9 Oxygen 0.6 CO 0.2

(b) When an identical fabric was used for the experiment described in Example (1a) without preceding heat and pressure treatment, so that it had lower resistance to liquid flow as indicated above, the following yields were obtained, expressed as percentages of the current applied:

The figures show that the use of the pressureand heattreated diaphragm leads to a considerable reduction in the amount of propylene glycol formed. Where the electrolytic cell is run with a recycled electrolyte, the effect of this reduction in glycol formation is that, where a polypropylene glycol level of 1.5% is adjusted in the recycled electrolyte, 2.3 t. of electrolyte per t. of propylene oxide produced have to be removed from the circuit if the nonheatand pressure-treated diaphragm is used, as against 0.6 t. when the presureand heat-treated diaphragm is used. a

This reduction in the quantity of electrolyte consumed is accompanied by a considerable decrease in the amount of effluent, which makes the process substantially more economical.

EXAMPLE 2 (a) The electrolytic cell described in Example 1 was used. A fabric produced from endless polypropylene filaments was used as the diaphragm which covered the cathode.

This fabric was guided between two rollers which were kept at a temperature of C. and which were pressed against one another under a linear pressure of kg./ cm. roller width. The rollers rotated at a uniform peripheral speed of 3.5 metres per minute. The changes which the fabric used underwent during the heat and pressure treatment are characterised by the following numerical data.

The throughfiow of a 5% aqueous potassium chloride solution through the diaphragm at room temperature amounted to 179 kg./drn. per hour before treatment and to 30 kg./dm. per hour after treatment at an excess pressure on the pressure side of a 200 mm. water column.

The experiment was carried out as described in Example 1. By applying a DC. voltage of 4.05 v., a current with a density of 10.9 amperes/dm. of apparent anode surface flowed through the cell. The yields of reaction product present in the anode spent gas and cathode spent gas and in the catholyte were as follows, expressed as percentages of the current converted:

Reaction product: Yield, percent Propylene oxide 88.4

1,2-dichloropropane 8.1 Propylene glycol 0.7 Propylene chlorohydrin 0.8 Other organic products 1.0 Oxygen 0.8

Reaction product: Yield, percent Propylene oxide 85.7

1,2-dichloropropane 8.0 Propylene glycol 3.4 Propylene chlorohydrin 0.9 Other organic products 0.9 Oxygen 0.9 CO 0.2

EXAMPLE 3 (a) The electrolytic cell described in Example 1 was used. A fabric produced from polyacylonitrile fibre yarn was used as the diaphragm which covered the cathode.

This fabric was passed between two rollers which were kept at a temperature of 210 C. and which were pressed against one another under a linear pressure of 160 kg./ cm. roller width. The rollers rotated at a uniform peripheral speed of 5.8 metres per minute. The following numerical data are intended to characterize the changes which the fabric underwent during the heat and pressure treatment. The throughfiow of a 5% aqueous potassium chloride solution at room temperature through the diaphragm, amounted to 144 kg./dm. per hour before treatment and to 2.9 kg./dm. per hour after treatment at an excess pressure on the pressure side of a 200 mm. water column.

The electrolytic cell was filled with a 5% aqueous potassium chloride solution of which 4 litres per hour were passed from the anode compartment through the diaphragm and the cathode into the cathode compartment. 27 Litres per hour of a C -fraction containing 95% of ethylene were introduced in gaseous form into the anode compartment through a frit arranged at the lower end of the anode plate. By applying a DC. voltage of 3.8 volts between anode and cathode, an electric current was passed through the cell in such a way that a current densitity of 10.6 A./drn. apparent anode surface was obtained. The temperature of the electrolyte was 52 C. The cell worked at atmospheric pressure. Approximately 30% of the ethylene passed through the anode compartment was converted. The yields of reaction products present in the spent cathode and anode gas and in the catholyte were as follows, expressed as percentages of the current converted.

Reaction product: Yield, percent Ethylene oxide 85.0

(b) When an identical fabric was used for the experiment described in Example (3a) without previous heatand pressure-treatment, so that it had the original resistance to liquid flow indicated above, the following yields were obtained:

Reaction product: Yield, percent Ethylene oxide 83.2 1,2-dichloroethane 6.2 Ethylene glycol 2.9 Ethylene chlorohydrin 6.0 Other organic products 0.7 Oxygen 0.7 CO 0.3

What we claim is:

1. In a process for the electrochemical conversion of olefins into olefin oxides in a system consisting of an anode, a cathode and a diaphragm arranged therebetween, using an aqueous electrolyte containing a metal halide wherein said electrolyte is passed from the anode compartment through the diaphragm into the cathode, compartment; the improvement which comprises using a diaphragm which consists of textile material, the liquid flow resistance of which is such that from about 2 kg. to 60 kg. per hour of a 5% aqueous potassium chloride solution pass through it per din. of its area at a temperature of about 20 C. at an excess pressure of about 200 mm. water column.

2. The improved process as claimed in claim 1 which comprises using a fibrous diaphragm containing thermoplastic material at least on the surface of the fibers thereof.

3. The improved process as claimed in claim 2, wherein said thermoplastic material is at least one member of the group consisting of a polyvinyl chloride, a copolymer of vinyl chloride and vinylidene chloride, a polyester, a polyamide, a polyolefin and a polyacrylonitrile.

4. The improved process as claimed in claim 2, wherein said textile material is subjected to a pressure until the required resistance to liquid flow is obtained to produce said diaphragm.

5. The improved process as claimed in claim 1, wherein the liquid flow resistance of said diaphragm is about 3.5 to 40 kg. per hour per dm.

6. The improved process as claimed in claim 1, wherein said textile fabric is subjected to a heat-treatment prior to use in said cell for a time suflicient to insure said liquid flow resistance.

7. The improved process as claimed in claim 1, wherein said textile fabric is subjected to a heatand pressuretreatment prior to use in said cell for a time sufiicient to insure said liquid flow resistance.

8. The improved process as claimed in claim 7, wherein the pressureand heat-treatment is carried out at a temperature which is about from 10 C.'to 150 C. below the softening point of the thermoplastic materials.

9. The improved process as claimed in claim 7, wherein the pressureand heat-treatment is carried out at a temperature which is about from 20 C. to 100 C. below the softening point of the thermoplastic materials.

References Cited UNITED STATES PATENTS 1,253,615 1/1918 McElroy 204-81 1,253,617 1/1918 McElroy 204- 1,308,797 7/1919 McElroy 204-80 3,288,692 11/1966 Le Duc 204-80 JOHN H. MACK, PrimaryExaminer H. M. FLOURNOY, Assistant Examiner U.S. Cl. X.R. 

